Grade: Grade 5 Subject: Science Unit: Cells Lesson: 5 of 6 SAT: Information+Ideas ACT: Science

Claim-Evidence Writing: Explaining Cells

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What is CER Writing?

Scientists don't just discover things - they have to explain their findings to others. CER is a framework that helps you write clear scientific explanations.

CER stands for Claim, Evidence, and Reasoning. Using this framework helps you think like a scientist and communicate your ideas clearly.

C Claim

A claim is your answer to a question or your main idea. It's a statement that can be supported with evidence.

Ask yourself: "What am I trying to prove or explain?"

E Evidence

Evidence is the data, observations, or facts that support your claim. Evidence comes from experiments, research, or observations.

Ask yourself: "What facts or data support my claim?"

R Reasoning

Reasoning explains WHY your evidence supports your claim. It connects your evidence to scientific principles.

Ask yourself: "Why does this evidence matter? How does it prove my claim?"

Memory Tip: Think of CER like a sandwich - the Claim is the top bun (your main point), Evidence is the filling (the tasty facts), and Reasoning is the bottom bun (holds it all together)!

Examples

Example 1: Comparing Plant and Animal Cells

Question: How are plant cells different from animal cells?

Claim:

Plant cells have structures that animal cells do not have, making them able to perform functions that animal cells cannot.

Evidence:

When observing cells under a microscope, I noticed that plant cells have a cell wall surrounding the cell membrane, large central vacuoles, and green chloroplasts. Animal cells lack all three of these structures.

Reasoning:

The cell wall provides extra support and protection, which is why plants can stand upright without bones. The large vacuole stores water and helps maintain the plant's structure. Most importantly, chloroplasts contain chlorophyll, which allows plants to make their own food through photosynthesis. Since animal cells don't have chloroplasts, animals must eat other organisms to get energy.

Example 2: The Importance of the Nucleus

Question: Why is the nucleus important for cell function?

Claim:

The nucleus is essential for cell survival because it controls all cell activities.

Evidence:

The nucleus contains DNA, which has the instructions for making proteins. In experiments where the nucleus was removed from a cell, the cell could no longer reproduce or make new proteins, and it eventually died.

Reasoning:

DNA acts like a blueprint or instruction manual for the cell. Without these instructions, the cell cannot make the proteins it needs to grow, repair itself, or carry out its functions. This shows that the nucleus is like the "brain" of the cell - without it, the cell cannot function properly or survive long-term.

Practice

Test your understanding of CER writing with these questions about cells.

Question 1: Which of the following is the best CLAIM for this question: "Why do cells need mitochondria?"

A) Mitochondria are found in both plant and animal cells.
B) Cells need mitochondria because they provide the energy required for all cell functions.
C) Mitochondria have their own DNA.
D) I observed mitochondria in my microscope lab.
Show Answer Explanation

Correct Answer: B

A good claim directly answers the question and can be supported with evidence. Option B states WHY cells need mitochondria (for energy). Options A and C are facts but don't answer "why cells need them." Option D is an observation, not a claim.

Question 2: Which is the best EVIDENCE to support the claim "The cell membrane is important for protecting the cell"?

A) The cell membrane is very thin.
B) I think the cell membrane is the most important organelle.
C) When scientists damaged the cell membrane in experiments, harmful substances entered the cell and the cell died.
D) Cell membranes are found in all cells.
Show Answer Explanation

Correct Answer: C

Good evidence comes from experiments, data, or specific observations. Option C describes an experiment that shows what happens without membrane protection. Options A and D are facts but don't show WHY it's important for protection. Option B is an opinion, not evidence.

Question 3: What does REASONING do in a CER paragraph?

A) States the main idea
B) Provides data from experiments
C) Explains why the evidence supports the claim
D) Asks a new question
Show Answer Explanation

Correct Answer: C

Reasoning is the "glue" that connects evidence to the claim. It explains WHY the evidence matters and how it proves the claim is correct. Option A describes a claim, Option B describes evidence.

Question 4: Read this CER response. Which part is MISSING? "Claim: Plant cells can make their own food. Evidence: Plant cells contain green chloroplasts that perform photosynthesis."

A) Claim
B) Evidence
C) Reasoning
D) Nothing is missing
Show Answer Explanation

Correct Answer: C

The response has a claim (plant cells can make their own food) and evidence (they have chloroplasts that do photosynthesis), but it's missing reasoning that explains WHY chloroplasts and photosynthesis allow plants to make food.

Question 5: Which statement is the best example of REASONING?

A) Cells are the basic unit of life.
B) The data shows that larger cells have more mitochondria.
C) This shows that cells need more energy producers as they grow, because larger cells require more energy to maintain their functions.
D) I counted 15 mitochondria in the cell.
Show Answer Explanation

Correct Answer: C

Reasoning explains "why" and "how." Option C explains WHY larger cells have more mitochondria (they need more energy). Options A and B are claims/evidence, and Option D is just data.

Question 6: A student writes: "Vacuoles are important. They are big in plant cells. Water is stored there." What should the student add to improve this as a CER response?

A) More facts about vacuoles
B) Reasoning explaining why water storage makes vacuoles important
C) A new claim about a different organelle
D) A question for the reader
Show Answer Explanation

Correct Answer: B

The student has a claim ("Vacuoles are important") and evidence ("big in plant cells, store water"), but needs reasoning to explain WHY storing water makes them important (e.g., water is needed for cell processes, maintains cell shape).

Question 7: Which question would be BEST answered using the CER format?

A) What is the name of the organelle that makes proteins?
B) How many cells are in the human body?
C) Why are mitochondria called the "powerhouse" of the cell?
D) When were cells first discovered?
Show Answer Explanation

Correct Answer: C

CER is best for "why" and "how" questions that require explanation. Option C asks "why," requiring a claim, evidence, and reasoning. The other options are factual questions with simple answers.

Question 8: In a CER about cell walls, a student writes evidence: "Plant cells have cell walls made of cellulose, which is a strong material." What would be good reasoning to add?

A) Cellulose is found in many plants.
B) Cell walls are outside the cell membrane.
C) Because cellulose is strong, it gives plants the rigid support they need to stand upright without a skeleton, which is why trees can grow so tall.
D) I observed cell walls in the lab.
Show Answer Explanation

Correct Answer: C

Option C connects the evidence (cellulose is strong) to the claim by explaining HOW this strength helps plants (rigid support, stand upright, grow tall). This is what reasoning should do - explain WHY the evidence matters.

Question 9: Which of these is NOT a good source of evidence for a CER about cells?

A) Data from a microscope observation
B) Results from a scientific experiment
C) Your personal opinion about cells
D) Information from a science textbook
Show Answer Explanation

Correct Answer: C

Evidence must be factual and verifiable. Personal opinions are not evidence because they cannot be proven with data or observations. Good evidence comes from experiments, observations, research, and reliable sources.

Question 10: A complete CER paragraph should include:

A) Only a claim and evidence
B) Only evidence and reasoning
C) A claim, evidence, AND reasoning that connects them
D) Just facts about the topic
Show Answer Explanation

Correct Answer: C

A complete CER needs all three parts: the Claim (your answer/main idea), Evidence (facts and data), AND Reasoning (explanation of why the evidence supports the claim). Missing any part makes the response incomplete.

Check Your Understanding

Key Questions to Consider

  1. Can you identify the claim, evidence, and reasoning in a scientific explanation?
  2. What makes evidence "good" versus "weak"?
  3. Why is reasoning important - can't evidence speak for itself?
  4. How does CER writing help you think more like a scientist?
Real Science Connection: Scientists use this same structure when writing research papers! Every scientific article has a claim (hypothesis/conclusion), evidence (data and results), and reasoning (discussion of what the results mean). Learning CER now prepares you for real scientific writing.

Summary

C

Claim

Your answer or main idea

E

Evidence

Facts and data that support your claim

R

Reasoning

Explains why evidence supports your claim

Next Steps

  • Practice writing your own CER paragraphs about cells
  • Review all cell structures and their functions
  • Prepare for the unit checkpoint to test your knowledge